The present invention relates to pulsed flame photometric detectors and the igniter assemblies associated therewith, and especially to portable detectors and the igniter assemblies associated therewith that are used in the field for onsite detection of trace amounts of chemical compositions. Such devices include a housing that contains and protects the detector and electrical power supply and an ionization chamber with one or more cables connecting the detector electronics and the ionization chamber to transmit power and electrical signals. One cable connects the electrical power supply to a filament located within the ionization chamber. The filament is heated by the passage of electrical current through the filament to ionize samples of chemical compositions that are injected into the ionization chamber. The ionized atoms of the chemical composition are detected and electrical signals indicative of the detected atoms are transmitted to the detector electronics to enable an operator to determine the composition of the injected chemical sample.
Operation of a pulsed flame photometric detector requires time for the detector to reach a steady state condition and for the ionization chamber, including the enclosed filament, to reach its operating temperature before a chemical sample can be injected into the ionization chamber for analysis.
A serious problem that limits effective use of portable pulsed flame photometric detectors is the power requirements necessary when utilizing standard filaments to achieve ionization. The use of a thicker wire as used in standard filaments has a great disadvantage of requiring more electrical power to ionize chemical samples. This requires a larger, heavier power supply, a disadvantage for a portable detector, and if the larger power supply is not selected, use of a smaller power supply shortens the time that the detector can be used. Use of thin wire filaments reduces the power requirements but it also reduces the lifecycle or longevity of the filament. A thin oxidation layer that forms on the filament during operation has provided some protection from degradation and from chemical attack, but this coating offers only limited protection for the filament.
Another problem is created by current designs in which the filament is attached to the end of a cable from the power supply. When the filament fails, the entire cable must be replaced. This requires that the device be completely opened up, giving the operator access to the detector body as well as the power supply so the filament and cable can be removed. For safety reasons, this may require some aspects of the instrument operation to be shut down. Following removal of the cable with the failed filament, a new cable with a new filament is installed. The pulsed flame photometric detector must then go through start-up and the time necessary to again reach steady state operating conditions. This is a severe problem when the detector is used in the field.
A pulsed flame photometer detector and methods for operating the detector are described in U.S. Pat. No. 5,153,673. The use of pulsed flame to combust or ionize a sample is described as is the use of detectors such as a thermionic ionization detector, an induced flourescence detector, an atomic absorption detector, an ion mobility spectrometer and a plasma emission detector for detecting the composition of the sample.
Coated filaments for other uses are also shown in the prior art such as the electric igniter construction shown in U.S. Pat. No. 3,810,734. However, in this patent, the coatings were selected for their ability to conduct electricity as well as their resistance to oxidation.